The invention relates to a sewing machine and more particularly relates to a system for adjusting the rotation phase of a pulse motor of a sewing machine, which is used to control the movement of the pattern utilized to adjust instrumentalities of the sewing machine in response to the control signals from the control circuit.
A pulse motor used as a pattern generator receives a driving pulse from the control circuit and is periodically driven within a predetermined drive range to actuate the needle bar, the feed controlling device and others so as to produce stitch patterns.
However, there will be chances of erroneous operation of the pulse motor at the starting time, since a stopping phase of the pulse motor is not correctly set when the electric power is supplied. Further in case the pulse motor steps out of normal adjustment during its operation due to some events, it must be recovered to the normal operation so as to prevent the subsequent wrong operations thereof.
For preventing the above mentioned erroneous operation of the pulse motor, there have been the methods of detecting the stopping phase of the motor or of once resetting the motor to a predetermined phase at the time of the initial power supply. The former is sufficient to use the potentiometer but this is problematical in the durability and cost. The latter is to drive the pulse motor to one direction until it is stopped by a stopper. But this latter case has the problems of shock, sound and durability, and may cause the disordered stepping movement of the motor during the operation which cannot be corrected by the above-mentioned methods.
This invention has been devised to eliminate the above mentioned defects involved in the prior art.